Such machines are known the concave disks of which have a spherical cap shape the edge of which is circular or notched. However, these known machines have several drawbacks.
A first drawback of the known machines resides in the fact that the smooth or notched disks cut weeds, which causes the weeds to proliferate. This proliferation is particularly great in the case of couch grass. The elimination of this increased mass of weeds requires a very large volume of weed-killing products, which increases production costs and dangers for the environment.
A second drawback of the concave disks equipping the known machines resides in the creation of a large plow sole which prevents the flow of water into the ground and the growth of the root system of the plants. Moreover, in clayey soils, the concave disks cause a considerable smoothing of clods, which is detrimental to their later breakup during the preparation of a seed bed. In addition, in clayey soils, the concave disks also have a tendency to clog very quickly. On the other hand, in loam soils, the concave disks cause a pulverizing of the soil which promotes the formation of extremely hard, harmful layers after precipitations.
A third drawback of the known machines resides in the fact that, in dry soils, the concave disks penetrate into the soil with much difficulty, or even do not penetrate at all.
A fourth drawback of the known machines relates to the relatively rapid wear of the concave disks. Since the concave disks cut the soil, their thickness must necessarily be relatively small. However, this thinness causes rapid wear.